Methods, communication devices and communication terminal devices of a generic type are used in the prior art. The communication devices and communication terminal devices serve to provide one or more communication connections between the at least two communication devices that are connected to the respective communication line.
The communication lines are formed by an electrical cable including corresponding electrical lines that may serve for transferring electrical signals, e.g. the communication signals. The lines may be for example two-wire or stranded lines that are utilized specifically for providing communication connections. However, the lines may also be power supply lines that may, in addition to transferring electrical power, also serve to make a hard-wired communication connection. The communication line may utilize at least two electrical conductors that serve to allow the electrical signals to be transferred.
In order to improve the channel capacity of the hard-wired communication connection that is provided by the communication line, the communication connection may include a multiple-channel form by, for example, utilizing carrier frequency systems. Communication signals are transmitted such that signal carriers, in some cases also called carrier signals or just carriers, are provided by which mutually independently usable channels of the hard-wired communication connection may be provided such that a multiple-channel hard-wired communication connection is made possible.
The signal carriers provide the electrical signals that are directly applied to the communication line or its electrical lines. In this context, a signal carrier may be formed by a periodically varying variable such as an alternating current voltage, an electromagnetic wave, an alternating current and/or similar. The variable may have constant characteristic parameters such as a frequency, amplitude, duty cycle, phase angle and/or similar. Consequently, signal carriers are used so that the communication signals may be transferred over the respective one of the communication lines as useful signals, for example by a carrier frequency method or similar.
To provide the communication signals to be transferred by the signal carriers, the signal carriers may be modulated by a modulation method, predetermined by the communication protocol, in accordance with the communication signals. On the transmission side, the modulation may be performed by a transmitting device that includes a suitable modulator. On the transmission side, the thus modulated signal carriers may be applied to the communication line, for example by the transmitting device of a first one of the at least two communication terminal devices or similar, that emits the communication signals.
The at least one second one of the communication terminal devices, that receives the modulated signal carriers, may receive the signals using a suitable receiving device and demodulate the signals appropriately, by the modulation method predetermined by the communication protocol, using a suitable demodulator of the receiving device, with the result that the communication signals originally for transmission are available again at the second communication terminal device. The communication connection formed in this way need not only be unidirectional but—depending on the communication protocol—may also take a bidirectional form, for example in the manner of a full duplex method or similar. The communication terminal devices are configured for this purpose. The communication terminal devices may each include a transmitting device and a receiving device.
In order to provide a respective channel of the multiple-channel hard-wired communication connection, the communication protocol provides for each of the channels of the multiple-channel hard-wired communication connection to have associated with each of the channels individually at least one of the signal carriers. As a result, communication channels may be created that may be utilized almost independently of one another for the purpose of communication between the at least two communication terminal devices. For example, orthogonal signal carriers may be utilized for this purpose. The orthogonality may also be produced by the modulation method or similar.
Moreover, a communication channel may include more than one of the signal carriers individually associated with it. Furthermore, during normal operation the association of the signal carriers with respective ones of the channels may be varied, in dependence on the communication load. The communication protocol may include appropriate controls making it possible for the communication terminal devices to adjust the association of the signal carriers with the respective channels as appropriate.
The most diverse modulation methods may be used as the modulation method, for example amplitude modulation, frequency modulation or indeed orthogonal frequency-division multiplexing (OFDM), quadrature amplitude modulation (QAM), phase modulation, combinations thereof or similar. Both analog and digital modulation methods, and combinations thereof, may of course be provided.
Generic methods and communication devices and communication terminal devices thus also relate among other things to field bus systems. A field bus is a bus system that couples field devices such as sensing probes, sensors, actuators and/or similar such that the devices communicate within a single system, for example with a control device that may be for example an automation device or similar. At least one communication line may provide a hardware coupling between the field devices and the control device. In order to guarantee communication over the communication line such that there is undisrupted communication between the field devices and the control device. There may also be a communication protocol that controls or establishes which technology is used as the basis and which properties are utilized for communication between the field devices and the control device. A field bus system may for example be an asymmetric digital subscriber line (ADSL), a wireless local area network (WLAN), or a powerline such as HomePlugAV, HomePlugGP or similar. As systems become more and more widespread, the separation of different networks, segments, and for example, communication lines gains in importance.
When hard-wired communication connections, for example multiple-channel hard-wired communication connections, are used line lengths, discontinuities and discontinuities in the routing of the communication lines, including mismatches of the communication lines, may result in reflections. In electrical engineering, this is dealt with in the context of line matching.
Line matching is based on the idea that a characteristic impedance may be associated with an electrical cable, for example, an electrical line. There is matching if, at a line end of a respective one of the communication lines, a connected device provides an impedance substantially corresponding to the characteristic impedance. By contrast, if the impedance differs from the characteristic impedance of the electrical line, reflections may be produced causing standing waves to be formed, for example, at frequencies whereof the wavelength is an integer multiple of a multiple of the line length of the communication line, or of a line section with a mismatched end.
When such frequencies are used as signal carriers, the result may be pronounced crosstalk or feed over between neighboring segments, such as other communication lines, and between signal carriers or channels. With high frequencies a relatively great amount of crosstalk or feed over is to be expected, because multiples of the kind mentioned above occur more densely, and there may be integer multiples for any long line length, for example of several meters or similar. In a range equating to several wavelengths of the line length, it is frequently the case that only inferior quality may be achieved, with the result that the wavelengths may be excited over a broad bandwidth. For general electrical engineering principles relating to electrical lines, the reader is therefore also referred to Nachrichtentechnik [Communications Engineering], third edition, Volume II, Nachrichtenübertragung [Message Transfer] by W. Ruprecht, Springer Verlag 1982, or similar.
It is already known to reduce or avoid crosstalk or feed over by line ends terminating with appropriate matching. Moreover, with signal carriers utilizing high frequencies, modulation with a relatively low modulation depth—for example with reduced amplitude—may be provided by the communication signal. In this way, for example with a field bus system such as HomePlug, for the purpose of observing standards relating to electromagnetic compatibility, with a frequency of the signal carrier higher than 28 MHz it is typically provided for the power utilized to be reduced by approximately 30 dB. This takes into account the fact that under the above-mentioned applicable standards interfering radiation is only measured from a frequency greater than 30 MHz.
Moreover, it is known to utilize frequency division multiplexing for example in powerline systems to avoid crosstalk or feed over between neighboring segments, or to better achieve the crossover segments or overlapping areas described there. Different frequency bands may be utilized on different lines.
Thus, the communication line needs to have not only two electrical lines but may moreover have further electrical lines, e.g. pairs of electrical lines, of a cable that may be utilized for the provision of the communication connection. In this case, a pair of lines may for example form a segment.